1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device including an oxide semiconductor.
In this specification, a semiconductor device means all types of devices which can function by utilizing semiconductor characteristics, and an electro-optical device, a semiconductor circuit, and an electronic device are all semiconductor devices.
2. Description of the Related Art
A technique for forming a transistor by using a semiconductor thin film formed over a substrate having an insulating surface has attracted attention. Such a transistor is applied to a wide range of electronic devices such as an integrated circuit (IC) or an image display device (display device). As a semiconductor thin film applicable to the transistor, a silicon-based semiconductor material is widely known. Moreover, an oxide semiconductor has been attracting attention as another material.
For example, a transistor whose active layer includes an amorphous oxide containing indium (In), gallium (Ga), and zinc (Zn) and having an electron carrier concentration of lower than 1018 /cm3 is disclosed (see Patent Document 1).